zAuction enables sale and auction of Ethereum NFTs.
The zAuction solidity contracts interact with the auction at only the level of the finalizing transaction, requiring only a single on-chain tx to complete one auction. The main benefit being that bids don't cost gas, so a popular NFT can receive as many bids as it needs without prohibitive bid costs.
This follows the philosophy that eth mainnet transactions should happen at the time of guaranteed value transfer, as opposed to tx's when a user isn't sure of the profit potential, such as a bid.
Users are free to participate in whatever auction process they want off-chain, and exchange appropriate finalizing signatures, with the WETH-receiving party submitting the single tx in the end to validate and exchange the NFT.
Anybody can provide a service to hold arbitrary auctions, we provide an auction service in zNS, using infura and mongoDB storage to manage bid data. The use of a centralized database to manage bids is a temporary scaling solution to improve upon the fleek IPFS storage solution that existed prior. While this was decentralized it simply couldn't meet scaling demand. When higher scalability is achieved on Ethereum network itself using Layer 2 solutions, we will be able to move back to a decentralized model.